202 



OSTEOLOGY 





and is in relation, by its lower part, with the transverse scapular vessels. This 

 surface, at the junction of the curves of the bone, is also in relation with the brachial 

 plexus of nerves and the subclavian vessels. It gives attachment, near the sternal 

 extremity, to part of the Sternohyoideus; and presents, near the middle, an oblique 

 foramen directed lateralward, which transmits the chief nutrient artery of the 

 bone. Sometimes there are two foramina on the posterior surface, or one on the 

 posterior and another on the inferior surface. The inferior or subclavian surface is 

 bounded, in front, by the anterior border; behind, by the subclavian border. 

 It is narrowed medially, but gradually increases in width laterally, and is contin- 

 uous with the under surface of the flat portion. On its medial part is a broad 

 rough surface, the costal tuberosity (rhomboid impression), rather more than 2 cm. 

 in length, for the attachment of the costoclavicular ligament. The rest of this 

 surface is occupied by a groove, which gives attachment to the Subclavius; the 

 coracoclavicular fascia, which splits to enclose the muscle, is attached to the margins 

 of the groove. Not infrequently this groove is subdivided longitudinally by a 

 line which gives attachment to the intermuscular septum of the Subclavius. 



The Sternal Extremity (extremitas sternalis; internal extremity). The sternal 

 extremity of the clavicle is triangular in form, directed medialward, and a little 

 downward and forward; it presents an articular facet, concave from before back- 

 ward, convex from above downward, which articulates with the manubrium sterni 

 through the intervention of an articular disk. The lower part of the facet is con- 

 tinued on to the inferior surface of the bone as a small semi-oval area for articula- 

 tion with the cartilage of the first rib. The circumference of the articular surface 

 is rough, for the attachment of numerous ligaments; the upper angle gives attach- 

 ment to the articular disk. 



The Acromial Extremity (extremitas acromialis; outer extremity). The acromial 

 extremity presents a small, flattened, oval surface directed obliquely downward, 

 for articulation with the acromion of the scapula. The circumference of the 

 articular facet is rough, especially above, for the attachment of the acromio- 

 clavicular ligaments. 



In the female, the clavicle is generally shorter, thinner, less curved, and smoother than in the 

 male. In those persons who perform considerable manual labor it becomes thicker and more 

 curved, and its ridges for muscular attachment are prominently marked. 



Structure. The clavicle consists of cancellous tissue, enveloped by a compact layer, which 

 is much thicker in the intermediate part than at the extremities of the bone. 



Ossification. The clavicle begins to ossify before any other bone in the body; it is ossified 

 from three centers viz., two primary centers, a medial and a lateral, for the body, 1 which appear 

 during the fifth or sixth week of fetal life; and a secondary center for the sternal end, which 

 appears about the eighteenth or twentieth year, and unites with the rest of the bone about the 

 twenty-fifth year. 



The Scapula (Shoulder Blade). 



The scapula forms the posterior part of the shoulder girdle. It is a flat, trian- 

 gular bone, with two surfaces, three borders, and three angles. 



Surfaces. The costal or ventral surface (Fig. 202) presents a broad concavity, 

 the subscapular fossa. The medial two-thirds of the fossa are marked by several 

 oblique ridges, which run lateralward and upward. The ridges give attachment 

 to the tendinous insertions, and the surfaces between them to the fleshy fibers, 

 of the Subscapularis. The lateral third of the fossa is smooth and covered by the 

 fibers of this muscle. The fossa is separated from the vertebral border by smooth 

 triangular' areas at the medial and inferior angles, and in the interval between 

 these by a narrow ridge which is often deficient. These triangular areas and the 

 intervening ridge afford attachment to the Serratus anterior. At the upper part 

 of the fossa is a transverse depression, where the bone appears to be bent on itself 



1 Mall, American Journal of Anatomy, vol. v; Fawcett, Journal of Anatomy and Physiology, vol. xlvii. 



